Preoperative left ventricular systolic function is an important determinant of prognosis following aortic valve replacement for isolated chronic aortic regurgitation. Although patients with subnormal function are at a greater risk for death or heart failure, many such patients enjoy an excellent outcome postoperatively. A means of objectively assigning risk among patients with depressed systolic function is desirable. In the current study, we examined the prognostic value of the left ventricular regurgitant volume to end-diastolic volume ratio, an index which provides information concerning both the magnitude of the imposed volume load, that is, the regurgitant volume, as well as the left ventricular response to this load, the end-diastolic volume. We evaluated the results of aortic valve replacement in 59 patients with isolated severe chronic aortic regurgitation undergoing operation between February 1975 and August 1983. Several indices of preoperative left ventricular function were identified which were significantly associated with subsequent cardiac death and heart failure. These include both the left ventricular ejection fraction and the regurgitant volume to end-diastolic volume ratio (RV/EDV). Overall, survival was significantly reduced in patients with left ventricular dysfunction (EF plus/minus 0.45). Among such patients, an RV/EDV ratio plus/minus 0.25 was associated with a greater risk of death or heart failure. This observation suggests that the LV enlargement seen in these patients exceeds that which could be attributable to the regurgitant volume load and may reflect some degree of irreversible dysfunction placing them at higher risk. Therefore, the regurgitant volume of end-diastolic volume ratio may help assign risk among patients with comparable degrees of left ventricular dysfunction.